1. Field of the Invention
The invention relates to a device and method for monitoring a chemical reaction proceeding from a first state to a second state by emitting and detecting radiation, reflected or transmitted, at points of interest for a spectral signature of the material undergoing the chemical reaction.
2. Prior Art
Optical technology using a combination of solid state emitters and detectors has been in use for over 20 years to measure and detect materials and events, such as blood oximetry, blood glucose levels, bacterial levels, the presence of certain types of cancer, paint color, fluid transmission in delivery tubes, paint colors, weed discrimination in agriculture, dye purities and for various food processing quality control.
The fundamental technology used in most of these applications is spectroradiometry, whereby mostly visible and specific wavelengths are detected by reflection or transmission into a detector from a suitable emitter, and the resultant signal levels used in an algorithm to provide a suitable control output from the measurement system. For example, water and CO2 have absorption lines at 2002 and 2004 nm. Conventional spectroradiometers are designed to measure the spectral power distribution of various illuminants. Spectral signatures are specific combinations of reflected and/or transmitted and absorbed electromagnetic radiation at varying wavelengths which can uniquely identify an object. The spectral signature of an object is a function of incident electromagnetic radiation wavelength(s) and the object's material interaction with those section(s) of the spectrum. A material's black body radiation emission, surface finish and other factors all interact to produce a spectral signature. Measurements can be made with various instruments, including a task specific spectrometer or detectors sensitive to specific regions of interest.
In an example of oximetry, or the measurement of the percentage of oxygenated hemoglobin, the calculation is done in a system that calculates the ratio of oxygenated hemoglobin to total hemoglobin by reflective or transmissive spectral response at two distinct wavelengths, typically 660 nm and 940 nm. Because the spectral characteristics differ at those wavelengths, then a quantitative series of measurements can be made during the arterial pulse and using a well defined algorithm, the output can be calculated and displayed. The system that makes this measurement must deal with establishing the location of the arterial pulse, sampling multiple times during the pulse, dealing with noise issues caused by movement and ambient light and finally calculating the value and providing a digital readout. A byproduct is also the pulse rate. See the sample spectral curves in FIG. 5 for Hb and HbO2.
With the advent of more light sources and more sophisticated detection methods, it is possible to detect spectral characteristics outside of the visible range that can be used to identify even more materials and events, both organic and inorganic. When chemical reactions take place a spectral signature of the constituents may produce additional and repeatable new characteristics, either in the form of absorption or reflection characteristics or the shape of the spectral curves. In this case it is therefore possible to detect not only the fundamental materials but also the resultant reaction. It is important to note that the added factor of curve shape has been added to optical spectroscopy, which can be used to enhance the identification process. The spectral signature in this case is determined through the use of one or more light emitters and one or more suitable detectors in order to determine the spectral response. A change in a spectral signature therefore makes it possible to identify any of the resultant constituents. It is also possible to add fluorescent markers to the constituents in order to enhance the spectral effects, both inside and outside the visible spectrum, such as might be used with cell identification by adding photo sensitive proteins that attach themselves to the cell structure, or by adding certain fluorescent additives to organic reactions that appear or disappear as a result of the reaction. Another example is that it has been demonstrated that resin double bonds in acrylic materials disappear during the curing process, resulting in the reduction or elimination of an absorption band in the neighborhood of 1.6μ.